Receiving and understanding a voice communication received using a communications device while in a noise environment is problematic. Ambient or background noise near the receiver, the near-end, may at times approach or exceed the volume levels of the received speech causing a listener to be unable to understand the message.
Simply increasing the volume of the received speech is not very effective in increasing the intelligibility of the speech. Speech amplitude levels fluctuate throughout a sentence, from word to word, and even from syllable to syllable. Increasing the volume to compensate for a low amplitude portion of the speech may cause the receiver to clip when a high amplitude portion of the speech is received. Adjusting the volume to compensate for a high amplitude portion may render a subsequent portion having a low amplitude unintelligible.
U.S. Pat. No. 5,907,823 describes a dynamic range compression method which based on an instantaneous measurement of a received speech level or amplitude and an estimate of the ambient and far-end noise levels adjusts the received signal to enhance intelligibility. FIG. 1 shows a system according to the '823 patent. The dynamic range compression module receives (1) the received speech signal, (2) a signal indicating an estimate of the far-end noise level, and (3) a signal indicating an estimate of the near-end or ambient noise level. The dynamic range compression module performs a transform of the received speech according to the transform pattern shown in FIG. 2.
Several drawback in the prior art systems exist which poorly address the issue of rapid variations in speech volume and very low speech levels.
It will be appreciated that for simplicity and clarity of illustration, elements shown in the figures have not necessarily been drawn to scale. For example, the dimensions of some of the elements may be exaggerated relative to other elements for clarity. Further, where considered appropriate, reference numerals may be repeated among the figures to indicate corresponding or analogous elements.